vquic: silence -Wmissing-field-initializers for nghttp3/ngtcp2 callback tables

[vszakats]

To avoid a breakage in CI and curl-for-win builds on upstream updates
extending the callback lists. Each such breakage needed patching curl,
rolling these patches into curl-for-win, and doing it in near real-time,
to keep CI and builds working (and still causing some red CI jobs).

Bring calmness here by suppressing the warnings and allowing time to
extend the callback tables as/if needed and at a convenient moment.

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Also explored the option to dynamically setup the the callbacks, but
the libraries need a static callback table before nghttp3 v1.11.0+ and
ngctp2 v1.14.0+ which made this unnecessarily complex.

nghttp3 1.18.0 causing two pytests to fail.
Possibly due to ngtcp2/nghttp3#539. → PR #22402

[Copilot]

Pull request overview

This PR reduces build noise in the HTTP/3 (QUIC) implementation by locally suppressing -Wmissing-field-initializers warnings triggered by nghttp3/ngtcp2 callback table initializers, using the existing CURL_HAVE_DIAG-guarded diagnostic pragmas.

Changes:

• Wrap nghttp3_callbacks initializer in cf-ngtcp2.c with #pragma GCC diagnostic push/pop and ignore -Wmissing-field-initializers when supported.
• Apply the same suppression to the nghttp3 proxy callback table in cf-ngtcp2-proxy.c.
• Apply the same suppression to the ngtcp2 callback table in cf-ngtcp2-cmn.c.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

File	Description
lib/vquic/cf-ngtcp2.c	Silences -Wmissing-field-initializers around the nghttp3 callback table initialization (guarded by CURL_HAVE_DIAG).
lib/vquic/cf-ngtcp2-proxy.c	Silences -Wmissing-field-initializers around the nghttp3 proxy callback table initialization (guarded by CURL_HAVE_DIAG).
lib/vquic/cf-ngtcp2-cmn.c	Silences -Wmissing-field-initializers around the ngtcp2 callback table initialization (guarded by CURL_HAVE_DIAG).

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[vszakats]

Trying a different approach.

[Copilot]

Pull request overview

Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.

[Copilot]

Pull request overview

Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.

[Copilot]

Pull request overview

Copilot reviewed 3 out of 3 changed files in this pull request and generated 3 comments.

[Copilot]

Pull request overview

Copilot reviewed 3 out of 3 changed files in this pull request and generated no new comments.

Comments suppressed due to low confidence (3)

lib/vquic/cf-ngtcp2.c:397

• cb is a function-scope static callbacks struct that is written to on every call. If multiple nghttp3 connections are initialized concurrently from different threads, these writes race on shared state (undefined behavior), even though the assigned function pointers are constant.

Consider keeping the callbacks immutable (initialized once and never modified) or storing the callbacks struct in the per-connection ctx so each connection has its own instance and there are no shared writes.

  static nghttp3_callbacks cb = { 0 };
  int rc;

  if(ngtcp2_conn_get_streams_uni_left(ctx->qconn) < 3) {
    failf(data, "QUIC connection lacks 3 uni streams to run HTTP/3");

lib/vquic/cf-ngtcp2-proxy.c:612

• cb is a function-scope static callbacks struct that is written to on every call. If multiple nghttp3 connections are initialized concurrently from different threads, these writes race on shared state (undefined behavior), even though the assigned function pointers are constant.

Consider keeping the callbacks immutable (initialized once and never modified) or storing the callbacks struct in the per-connection ctx so each connection has its own instance and there are no shared writes.

  static nghttp3_callbacks cb = { 0 };
  int rc;

  if(ngtcp2_conn_get_streams_uni_left(ctx->qconn) < 3) {
    failf(data, "QUIC connection lacks 3 uni streams to run HTTP/3");

lib/vquic/cf-ngtcp2-cmn.c:891

• cb is a function-scope static callbacks struct that is written to on every call. If multiple QUIC connections are created concurrently from different threads, these writes race on shared state (undefined behavior), even though the assigned function pointers are constant.

Consider making the callbacks table immutable (initialized once and never modified) or storing it per-connection (in ctx) to avoid shared mutable state.

  static ngtcp2_callbacks cb = { 0 };
  static const struct alpn_spec ALPN_SPEC_H3 = { { "h3", "h3-29" }, 2 };

  DEBUGASSERT(ctx->initialized);
  ctx->dcid.datalen = NGTCP2_MAX_CIDLEN;

[Copilot]

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Copilot reviewed 3 out of 3 changed files in this pull request and generated no new comments.

[Copilot]

Pull request overview

Copilot reviewed 3 out of 3 changed files in this pull request and generated no new comments.